She was the first woman literary editor of the Westminster Gazette and in that capacity published the early work of such writers as Rupert Brooke, Graham Greene, Elizabeth Bowen, and Rose Macaulay.
[2] Royde-Smith rose from being a contributor to the editor of the "problems and prizes" page, a responsibility she shared with her sister Leslie (who would marry George Maitland Lloyd Davies).
[3][5][6] In the mid 1920s, Royde-Smith began writing the first of her novels, along with a few plays, biographies, and other works, an occupation that she was able to take up full time after the Gazette closed.
[3][8] The Tortoise-Shell Cat, which has been held to be her best book, is about a thwarted relationship between a young teacher and a predatory older woman; it has gone in and out of print several times.
[1][5] Later, in 1926, she married Ernest Milton, a London-based Italian-American actor who played many roles with the Old Vic from 1918 and who also appeared as Robespierre in Alexander Korda’s 1934 film of The Scarlet Pimpernel.
The character Aunt Evelyn in Rose Macaulay's 1926 novel Crewe Train—an intelligent, stylish, gossipy person of an interfering disposition—is said to have been a satire of Royde-Smith.